Clean up misc. formatting, `cursor` and `outline` styles
Clean up Buttons test page to be a very plain HTML page
Add Base to Menus test page
Improve `:focus` styles by making the same as `:hover` styles
Add back `cursor: not-allowed` for disabled buttons
Update styles for focused disabled Menu items to look disabled
Update HISTORY.md entries with more info on `:focus` changes
Merge pull request #86 from ericf/improve-focus

Improve `:focus` styles by making the same as `:hover` styles